Scientists agree climate change is one of the most serious issues facing humanity.

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But targets adopted today for curbing greenhouse gas emissions will determine whether the pattern stabilizes thereafter, or grows even worse.

High temperatures and heat waves in the last decade are widely blamed on climate change that occurred over the last 50 years -- amounting to global warming of about 0.5 degrees Celsius (0.9 deg Fahrenheit), said the study in the journal Environmental Research Letters.

And they are predicted to become harsher and more frequent as the Earth continues to warm over the course of the 21st century.

Based on climate modelling, the study projects that extreme heat waves like those that hit the United States in 2012 and Australia in 2009 will by 2020 affect about 10 percent of total land area -- double today's figure.

By 2040, it would have quadrupled.

"Over the same period, more extreme events will emerge: five-sigma events which are now essentially absent will cover a small but significant fraction (about three percent) of the global land surface by 2040," said the study.

Five-sigma events are described as "unprecedented" heat waves by the researchers and extreme events as three-sigma.

"In the first half of the 21st century, these projections will occur regardless of the amount of CO2 emitted into the atmosphere," said a statement by the Institute of Physics which publishes the journal.

But what happens after 2040 can still be influenced by what we decide now.

"Under a low emission scenario, the number of extremes will stabilize by 2040, whereas under a high emission scenario, the land area affected by extremes will increase by one percent a year" until three-sigma heat waves affect 85 percent of the global land area by 2100 and five-sigma events about 60 percent.

A low emission scenario would entail limiting the concentration of greenhouse gases in the atmosphere to 490 parts per million of CO2 equivalent before 2010, followed by a decrease, whereas the worst case scenario involves no change to current trends.

UN members have adopted a target of curbing warming to a maximum 2 degrees Celsius (3.6 deg Fahrenheit), and are negotiating a new treaty on carbon emissions targets that must be signed in 2015 and enter into force by 2020.

The negotiations have been slow and the yearly rise in emissions has led some scientists to conclude that warming of 3 or 4 degrees Celsius (5.4-7.2 deg Fahrenheit) is probable by century's end.